This invention relates to the field of magnetic recording. More particularly it relates to the recorder heads and the structural disposition thereof in a multitrack head.
In magnetic recording the use of thin film heads is well known. A thin film head generally designated by numeral 10 is shown in FIGS. 1 and 2 and comprises a bottom permalloy 20 formed on a substrate 30, with windings 40 provided on the permalloy. A top permalloy pole piece 50 is provided and is separated from the bottom permalloy layer by a selected gap 52. The windings 40 are connected to pads 42 wherein current driver 44 attaches. Insulation layers 60 are provided to insulate the windings 40 from adjacent permalloys 20 and 50. In operation, current from the current driver flows through the windings 40 to produce a magnetic field at the gap 52 that records magnetic spots on the magnetic tape or other recording medium 70.
The formation of the thin film head may be briefly described as follows: a silicon or ceramic substrate 30 is coated with a permalloy [NiFe] magnetic material 20. Then an insulating layer 60 of preferably silicon dioxide is formed on the permalloy. Next, aluminum or other conductor is deposited and patterned into windings 40 and this is followed by deposition of a second insulator 60. Optionally, a second patterned winding may be provided. For example, IBM produces a recording head using two layers of windings with four turns per layer, and "DASTEK" makes an improved recording head having five turns in one layer and four turns of the winding in another. After formation of the windings 40 the permalloy pole piece 50 is formed and situated connected at one of its ends 54 to the bottom permalloy 20 and separated from the bottom permalloy at its other end to provide the recording gap 52 as is well known in the art.
The largest use of such thin film recording head devices is for disk drives. Disk drives typically use a single head and move it across the disk. Some disk applications use a fixed head array. There are also some applications for the thin film heads in tape recorders but those that are used usually have two to four heads.
With the trend towards miniaturization, there is a need to record a lot of data in the smallest possible space on a recording medium such as magnetizeable tape. This is especially true where it is desired that the recording instrument use tapes of very narrow width, as for example with portable hand-held video cameras that utilize small cassettes with tape widths of less than a quarter of an inch wide.
It is possible to record a large amount of data on a tape of small width by running the tape at a very high speed but this would require an excessive length of tape. Additionally, at this high speed eddy currents and hysteresis losses begin to limit the usefulness of the recorded informtion and the usefulness of the head which must then be made of special material for use under such conditions. It is also possible to store a large amount of data by using fewer heads and moving the head along one track on the tape at a very fast speed, then stopping the tape and reversing the movement of the tape and positioning the head on a second track. That would require very fast movement and great precision in stopping and starting of the tape, inviting more problems with respect to ensuring the integrity of the recorded information.
Another option is to provide a plurality of heads across a tape, thereby increasing the number of tracks of data stored on the tape. However, although track separation need only be slightly larger than the gap length P, as shown in FIG. 3, in fact the track separation D is determined by the width of thin film head. As is apparent from FIG. 3 the pancake-like thin film head is much wider than the gap length P and consequently close packing of the tracks has not been obtainable heretofore. As a result the art has not been able to record a sufficient amount of video information on a tape which is relatively slow moving and narrow.